The present invention relates to a rotary solids feeder. In a more specific aspect the present invention relates to an improved rotary feeder for metering particulate materials and method of metering particulate materials.
In numerous operations it is often necessary to feed solid particulate materials to a reaction system or a blending operation in small quantities and with a high degree of accuracy. For example, solid particulate catalysts as well as solid chemical reactants are often added in small quantities. This is generally accomplished by the use of rotary solids feeders, of which there are numerous designs. Basically, such rotary feeders include a rotor mounted on a rotatable shaft and a sleeve-type housing surrounding the rotor and having its ends closed except for the passage of the shaft through one of the ends. The apparatus is usually mounted with the axes of the rotor and housing in a horizontal plane. An inlet is formed through the top of the sleeve portion and is fed with solid particulate material from a supply means. A diametrically opposed outlet is formed through the bottom of the sleeve portion and is connected to the system to which the particulate material is to be fed, usually by a simple conduit. At least one cavity is formed in the periphery of the rotor at a longitudinal position coinciding with the inlet and outlet openings of the housing. Accordingly, as the rotor rotates and the cavity passes the inlet opening it is filled with particulate material. This particulate material is then discharged through the outlet as the filled cavity passes the outlet. Usually there are two diametrically opposed cavities in the rotor so that as one cavity is being filled the other is discharging. Since the interior of the housing acts as a bearing surface for the rotor and the material being handled should not pass between the rotor and the housing, the fit between the two must be reasonably precise. Such close tolerance between the rotor and the housing, the very nature of the materials being handled and the characteristics of the feeder itself make it impossible to prevent some of the particulate material from passing between the rotor and housing. Consequently, when both the rotor and housing are made of metal rapid wear takes place. Accordingly, the rotor is often made of a hard resinous material, such as polyphenylenesulfide, tetrafluoroethylene, high density polyethylene, polychlorotrifluoroethylene, nylon, etc. and is mounted on the shaft and within the housing so as to be readily replaceable. Another alternative is to utilize a resinous material sleeve, which is also readily replaceable, as the inner bearing surface of the housing. Because of the close tolerance which is required between the rotor and housing and the tendency of the bearing surfaces to wear, rotors are also formed in a frusto-conical configuration and the interior of the sleeve portion of the housing is appropriately frusto-conical to receive such a rotor. To compensate for minor wear, the frusto-conical rotor can also be resiliently urged toward the minor opening of the housing. It has also been proposed to at least periodically force a fluid through the space between the bearing surfaces in order to flush out any particulate material which may collect in the space between the rotor and the housing.
While rotary solids feeders of the character described above are routinely utilized for feeding particulate materials and adequately perform the function for which they are designed, there are a number of instances in which problems are still encountered. In accordance with the present invention, it has been found that numerous particulate materials have a tendency to cake or agglomerate in the cavities of the rotor and, accordingly, fail to dump the particulate material properly. Obviously, such buildup of the particulate material in the cavities results in gross inaccuracies in the volume of material being fed, particularly where the quantity of material to be fed is extremely small. It was also found that such buildup is quite rapid, rendering the apparatus essentially useless for its intended purpose. Such caking or buildup can be caused by any number of factors, including the nature of the particulate material itself, the small particle size of the material, the necessity of feeding the material from the hopper to the rotary feeder under mechanical or fluid pressure and the like.
It is therefore an object of the present invention to overcome the above-mentioned problems, as well as other problems of the prior art devices.
Another object of the present invention is to provide an improved rotary solids feeder and method of metering solid, particulate materials.
Yet another object of the present invention is to provide a rotary solids feeder which will accurately meter particulate material.
Another and further object of the present invention is to provide a rotary solids feeder which prevents the collection or buildup of solid particulate material within the cavities of the rotor.
Still another object of the present invention is to provide an improved rotary solids feeder wherein substantially all of the solid particulate material to be fed is removed from the cavity of the rotor each time the cavity passes the outlet of the feeder.
These and other objects and advantages of the present invention will be apparent to one skilled in the art from the following description.